Acoustic generator and associated methods and well systems

ABSTRACT

A well system and associated method can include an acoustic generator which can be used to excite a formation with acoustic waves transmitted from the acoustic generator. Another well system and associated method can include an acoustic generator which can transmit acoustic waves into cement surrounding a casing. Another well system and associated method can include an acoustic generator which can be used to transmit acoustic waves into an annulus surrounding a well screen during or after a gravel packing operation. Another well system and associated method can include an acoustic generator which can be connected in a drill string in close proximity to a drill bit, with the acoustic generator transmitting acoustic waves into a formation ahead of the bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of prior application Ser. No. 12/834,971filed on 13 Jul. 2010, which claims the benefit under 35 USC §119 of thefiling date of provisional application No. 61/225,311 filed on Jul. 14,2009. The entire disclosures of these prior applications areincorporated herein by this reference.

BACKGROUND

This disclosure relates generally to equipment utilized and operationsperformed in conjunction with a subterranean well and, in an exampledescribed below, more particularly provides an acoustic generator andassociated methods and well systems.

Hydrocarbons in the earth are generally contained within pores offormation rock having varying degrees of permeability. Sometimes thehydrocarbons do not readily flow toward a wellbore for production forvarious reasons, such as, low formation permeability, high viscosity,etc.

In the past, hydraulic fracturing has been used to form fractures informations and thereby expose more surface area of the formations, andstimulation treatments (such as acidizing, etc.) have been used toenhance flow of hydrocarbons from formations to wellbores, but thesetechniques have disadvantages. For example, hydraulic fracturingrequires large quantities of fluid to be pumped into a formation, theresulting fractures can unintentionally intersect undesirable zones(such as water or gas zones), very specialized and expensive surfaceequipment is required for fracturing and acidizing, etc.

Therefore, it may be seen that improvements are needed. The improvementsdescribed below can be useful in enhancing flow of hydrocarbons or otherfluids, investigating formation characteristics, communicating in wells,and for other purposes.

SUMMARY

In the disclosure below, a downhole acoustic generator and associatedmethods and well systems are provided to the art. One example isdescribed below in which an acoustic generator is used to enhanceproduction of fluid into a wellbore. Another example is described belowin which an acoustic generator is used to investigate characteristics ofa formation.

In one aspect, a well system and associated method are provided in whichan acoustic generator is used to excite a formation with acoustic wavestransmitted from the acoustic generator.

In another aspect, a well system and associated method are provided inwhich an acoustic generator transmits acoustic waves into cementsurrounding a casing. The casing may be coated with a hardening agent,or the hardening agent may be contained in containers. The casing may berun into the well, the cement may be pumped into place in an annulus,and then the hardening agent may be mixed with the cement using acousticwaves transmitted by an acoustic generator. The hardening agent may bedispersed and mixed with a cement using an acoustic generator, no matterwhat release mechanism is used. The hardening agent may be released as aresult of heating the cement using acoustic waves, and/or the cement maybe cured using heat from the acoustic waves.

In yet another aspect, a well system and associated method are providedin which an acoustic generator is used to transmit acoustic waves intoan annulus surrounding a well screen during or after a gravel packingoperation.

In a further aspect, a well system and associated method are provided inwhich an acoustic generator is connected in a drill string in closeproximity to a drill bit, the acoustic generator transmitting acousticwaves into a formation ahead of the bit.

Another aspect includes a well system and method in which acoustic wavesare transmitted into a formation during a fracturing process whichincludes proppant, thereby increasing depth of penetration and/ordensity of proppant (e.g. sand, ceramics, etc.) flowed into thefracture(s), resulting in increased or deeper propping and increasedconductivity of the propped fracture(s).

Another aspect includes a well system and method in which acoustic wavestransmitted into a formation increases wetting and mixing of conformanceagents such as relative permeability modifiers, thereby improvingrejection of water and/or gas from entry to the near wellbore region orfractures in the formation and improving oil production or productionratios.

Another aspect includes a well system and method in which acoustic wavesare transmitted into a formation near a zone of production or higher,semi-permanently for inhibition or as an intervention for remediation,of flow assurance problems such as hydrates, scale, wax, or asphaltineformations, in the near well production zone or in a completion ortubulars.

The acoustic generator can include a vibration isolation device (e.g., ahigh damping material, mechanical filter, etc.) between the acousticgenerator and the string on which it is conveyed, to protect the string.The acoustic generator may be used in conjunction with an isolatorsection of casing, or such section of other tubular strings, which areabove or below the zone in which the device is intended to be used, tosimilarly reflect or attenuate the acoustic energy traveling up or downthe wellbore with potentially negative effects. Elastomeric packers maybe preferred to bound the zone being acoustically stimulated, havingnatural damping tendencies. The system may include one or more sensorswithin, or proximate, or distant, from the acoustic generator for realtime feedback of its output, and/or vibratory response of intendedtarget and/or of elements not desired to be excited, for real timetuning of amplitude, frequency, etc.

Also provided is a well system and method in which, while stimulatingvia one wellbore, returns are taken from an adjacent wellbore, wherebypore pressure relief attracts a propagation plane toward the adjacentwellbore. Controlled pore pressure relief can enhance the effect of theacoustic waves.

A well system and method are also provided in which, after a well isinitially fractured, an acoustic generator is used to excite orre-excite an existing fracture geometry.

A further well system and method are provided in which a formation isexcited by acoustic waves generated by an acoustic generator in severalplaces across a generally horizontal wellbore, whereby the position orareas where a steam chamber develops in a SAGD system is selected.

These and other features, advantages and benefits will become apparentto one of ordinary skill in the art upon careful consideration of thedetailed description of representative examples below and theaccompanying drawings, in which similar elements are indicated in thevarious figures using the same reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cross-sectional view of a well systemand associated method which embody principles of the present disclosure.

FIG. 2 is a schematic partially cross-sectional view of the well system,in which fluid is received into a wellbore from a formation.

FIG. 3 is a schematic partially cross-sectional view of anotherconfiguration of the well system.

FIGS. 4A & B are schematic partially cross-sectional views of anotherconfiguration of the well system, with acoustic waves being transmittedinto the formation in FIG. 4A, and fluid being received from theformation in FIG. 4B.

FIG. 5 is a schematic partially cross-sectional view of anotherconfiguration of the well system.

FIG. 6 is a schematic cross-sectional plan view of a distribution ofwellbores which may be used in the well system.

FIG. 7 is a schematic lateral cross-sectional view of a distribution ofwellbores which may be used in the well system.

FIG. 8 is a schematic lateral cross-sectional view of anotherdistribution of wellbores which may be used in the well system.

FIG. 9 is yet another schematic lateral cross-sectional view of adistribution of wellbores which may be used in the well system.

FIG. 10 is a schematic partially cross-sectional view of anotherconfiguration of the well system.

FIG. 11 is a schematic partially cross-sectional view of yet anotherconfiguration of the well system.

FIG. 12 is a schematic elevational view of a manner of delivering fueland oxidizer to an acoustic generator in the well system.

FIG. 13 is a schematic elevational view of another manner of deliveringfuel and oxidizer to an acoustic generator in the well system.

FIG. 14 is a schematic partially cross-sectional view of a furtherconfiguration of the well system.

FIG. 15 is a schematic partially cross-sectional view of anotherconfiguration of the well system.

FIG. 16 is a schematic partially cross-sectional view of anotherconfiguration of the well system.

DETAILED DESCRIPTION

Representatively illustrated in FIG. 1 is a well system 10 andassociated method which embody principles of this disclosure. In thewell system 10, an acoustic generator 12 is conveyed into a wellbore 14and is used to transmit acoustic pressure waves 16 into a zone orformation 18 surrounding the wellbore.

One of the purposes of the acoustic generator 12 in the system 10 is toeliminate the need for hydraulic fracturing in traditional porous typereservoirs, as well as shale structure formations. However, hydraulicfracturing could be used, without departing from the principles of thisdisclosure.

The acoustic generator 12 creates near-field and far-field stimulationeffects within the rock matrix of the formation 18. In this scenario,the acoustic generator 12 could be deployed in a producing well (new orpreviously on production), with the intent of using the acoustic energyof the acoustic waves 16 to disturb and agitate the rock matrix, therebycreating new and enhanced conductivity which enhances the flow ofhydrocarbon fluid 20 toward the wellbore 14.

Stimulation fluids (such as acid, etc.) can be flowed into the formation18 from the wellbore 14 while the acoustic generator 12 transmits theacoustic waves 16 into the formation. In this manner, distribution andpenetration of the stimulation fluids into the formation 18 can beenhanced.

Acoustic waves 16 transmitted into the formation 18 during a fracturingprocess which includes proppant can increase depth of penetration and/ordensity of proppant (e.g. sand, ceramics, etc) into the fracture(s),resulting in increased or deeper propping and increased conductivity ofthe propped fracture(s). The acoustic waves 16 can be “tuned” to aresonant frequency of the proppant.

In FIG. 2, the system 10 is representatively illustrated after theacoustic waves 16 have stimulated flow of the hydrocarbon fluid 20toward the wellbore 14, with the acoustic generator 12 retrieved fromthe well. In a similar method, acoustic generators 12 could be deployedin a well grid strategy (similar to a “5 spot” steamflood design) wherewellbores 14 having acoustic generators 12 deployed therein aresurrounded by producing wellbores 22 (see FIG. 6, shown from a planview). The acoustic generators 12 can continue to transmit acousticwaves 16 into the formation 18 while the hydrocarbon fluid 20 isproduced from the wellbores 22 surrounding the wellbores 14 in which theacoustic generators are deployed.

Acoustic energy increases wetting and mixing of conformance agents suchas relative permeability modifiers, to improve rejection of water or gasfrom entry to the near wellbore region or fractures in the formation andthereby improve oil production or production ratios.

This strategy could be used in horizontal or vertical constructedwellbores. The acoustic energy emanating from the wellbores 14 in whichthe acoustic generator(s) 12 are deployed excites the natural rockmatrix and enhances hydrocarbon recovery into the producing wellbores 22(see FIG. 7, in which the wellbores 14, 22 are generally horizontal andlaterally spaced apart).

The process could also be used in a multilateral well design from asingle surface location where certain laterals (such as wellbore 14, asdepicted in FIG. 8) have the acoustic generator 12 deployed therein andother wellbores 22 are used for producing hydrocarbon fluids 20 to thesurface. In all of these scenarios, the acoustic generators 12 could beremedially or temporarily deployed within the wellbores 14 using coiledtubing or jointed pipe, or could be permanently installed in thewellbores.

In FIG. 9, a combination of the methods described above is used, inwhich the wellbores 14, 22 are generally horizontal and are laterallyspaced apart, with the producing wellbores being multilaterals. Anyconfiguration of producing wellbores 22 and wellbores 14 having theacoustic generator 12 deployed therein may be used, in keeping with theprinciples of this disclosure.

In FIG. 3, the acoustic generator 12 is conveyed into the wellbore 14which is lined with casing 24 cemented in the wellbore with cement 26 inan annulus 28 formed between the casing 24 and the wellbore. Aproduction tubing string 30 is positioned within the casing 24 andterminates above perforations 32 extending through the casing and cement26, and into the formation 18.

An adjacent producing wellbore 22 may be similarly configured withcasing 24, cement 26, tubing string 30 and perforations 32. However, itshould be clearly understood that it is not necessary in keeping withthe principles of this disclosure for any of the wellbores 14, 22 tohave a particular configuration. For example, any of the wellbores 14,22 could be uncased or open hole, in which case the casing 24, cement 26and perforations 32 may not be used.

The acoustic generator 12 is depicted in FIG. 3 as being conveyed on atubing string 34 (such as a coiled tubing string), but any type ofconveyance may be used in any of the configurations of the well system10 described herein. For example, wireline, casing, liner, jointedtubing, downhole tractors, or any other type of conveyance may be used.

The acoustic generator 12 may be any type of acoustic pressure wavegenerator. The acoustic generator 12 could generate the acoustic waves16 due to combustion therein (e.g., by oxidation of a fuel), theacoustic generator could be electrically powered (e.g., usingpiezoelectric elements, magnetostrictive elements, voice coil orsolenoid, a motor, etc.), the acoustic generator could be fluid powered(e.g., using a pressure pulse generated by discharge of fluid from anaccumulator, selective cavitation in a fluid flow, otherwise generatedpressure pulses such as via the Pulsonics™ tool available fromHalliburton Energy Services, Inc.), the acoustic generator could utilizean acoustic dipole (e.g., wherein fluid is alternately discharged andreceived in a chamber), and the acoustic generator could be positionedat any location (e.g., downhole, at the earth's surface, subsea, etc.).

The acoustic generator 12 may include a vibration isolation device(e.g., high damping material, or mechanical filter) between the acousticgenerator and the string on which it is conveyed, to protect the string.

The acoustic generator 12 may be used in conjunction with an isolatorsection of casing, or such section of other tubular strings, which areabove or below the zone in which the device is intended to be used, tosimilarly reflect or attenuate the acoustic energy traveling up or downthe wellbore with otherwise potentially negative effects.

Elastomeric packers may be preferred to bound the zone beingacoustically stimulated, with the packers having natural dampingtendencies.

The system 10 may include one or more sensors 33 within, or proximate,or distant from, the acoustic generator 12 for real time feedback of itsoutput, and/or vibratory response of intended target and/or of elementsnot intended to be excited, for real time tuning of amplitude,frequency, etc.

In steamflood or waterflood operations (or other types of conformanceoperations), use of the acoustic generator 12 can enhance distributionand penetration of the steam, water or other fluids through theformation 18. In that situation, the acoustic generator 12 couldtransmit the acoustic waves 16 into the formation 18 while the fluid(water, steam, etc.) is injected from the wellbore 14 into theformation.

Acoustic energy may be transmitted into the formation during afracturing process which includes proppant, to increase depth ofpenetration and/or density of proppant (e.g. sand, ceramics, etc) intothe fractures. This can result in increased or deeper propping andincreased conductivity of the propped fractures.

Use of the acoustic generator 12 can enhance injectivity anddistribution of certain treatment fluids within a reservoir matrix. Amore uniform distribution of conformance (e.g., sealants, relativepermeability modifiers, etc.) and/or acidizing chemicals would mostcertainly increase the overall effectiveness of the treatment processand reduce the chemical requirements.

In this case, the acoustic generator 12 could be deployed into thewellbore 14 using a jointed or coiled tubing workstring 34. The acousticwaves 16 could be transmitted into the formation 18 before the treatmentfluid is pumped or in stages during the treatment process.

The acoustic waves 16 will agitate the surrounding matrix of theformation 18 which will ensure a more uniform distribution of thetreatment/stimulation fluids. A similar process could be used inconjunction with a reservoir sweep process using water, natural gas orsteam to effectively remove hydrocarbon fluids 20 from the reservoirporosity, which enhances the depletion efficiency.

Whether utilized for enhancement of production, injection, stimulation,or any other type of operation, the acoustic waves 16 can be “tuned” toa resonant frequency of the casing 24. For example, the acousticgenerator 12 can be set to generate the acoustic waves 16 at a resonantfrequency of radial and/or transverse modes of vibration for the casing24. Preferably, the acoustic waves 16 are generated at a frequency whichis at or below a resonant frequency of the casing 24.

In other examples, the acoustic generator 12 can be set to generate theacoustic waves 16 at a resonant frequency of the formation 18 fluidsystem (e.g., the pores in the formation rock, interconnecting passages,the fluid therein, etc.), at a resonant frequency of the formation rockitself, or at a frequency which results in maximum transfer of energy toan intended target. For example, if it is desired to transfer a maximumamount of acoustic energy to the formation 18, to the cement 26 (e.g.,to reduce voids in the cement, to release a hardening agent into thecement, etc.) or to another element, the acoustic generator 12 can beoperated to transmit a range or “sweep” of acoustic frequencies, and asensor 33 (such as an accelerometer) can be used to determine which ofthe acoustic frequencies results in maximum transfer of acoustic energyto the element.

The sensor 33 can be used in any of the configurations of the wellsystem 10 described herein. The sensor 33 can measure a response of anycomponent of the system 10 (such as, the formation 18, the casing 24,the cement 26, a gravel pack, a well screen, etc.) to the transmittedacoustic waves 16.

In FIG. 4A, the acoustic generator 12 is relatively permanentlyinstalled in the wellbore 14. The acoustic waves 16 are periodicallytransmitted into the formation 18 by the acoustic generator 12. When theacoustic waves 16 are not being transmitted, the fluid 20 is producedfrom the formation 18, as depicted in FIG. 4B.

Thus, stimulation of the formation 18 by the acoustic waves 16 isalternated with production of the fluid 20 from the formation, with thesame wellbore 14 being used for deployment of the acoustic generator 12and for production of the fluid 20. In other examples, the formation 18may be stimulated by the acoustic waves 16 while the fluid 20 isproduced. In further examples, separate wellbores 14, 22 may be used fordeployment of the acoustic generator 12 and for production of the fluid20.

In the system 10 of FIGS. 4A & B, the acoustic generator 12 is of thecombustion type. Lines 36, 38 are used to flow fuel and oxidizer to theacoustic generator 12 from a remote location, such as the surface. Thelines 36, 38 are depicted in FIGS. 4A & B as being positioned betweenthe tubing 30 and casing 24, but they could be otherwise positioned(such as internal to the tubing, in a wall of the tubing or casing,etc.).

A suitable combustion-type acoustic generator is described in U.S.Publication No. 2009/0008088, the entire disclosure of which isincorporated herein by this reference. A steam generator which generatessteam for use in generating acoustic signals 16 may be supplied withheat by, for example, combustion of fuel or electrical resistanceheating.

In FIG. 5, the acoustic generator 12 is relatively permanently installedin the wellbore 14, and the fluid 20 is produced from an adjacentwellbore 22 via production tubing 30. The acoustic waves 16 may becontinuously transmitted into the formation 18, or the acoustic wavesmay be periodically transmitted or pulsed.

In the above examples of the system 10, hydraulic fracturing may not beused at all to stimulate production of the fluids 20 from the formation18. However, it is contemplated that benefits could be obtained by usingthe acoustic generator 12 to transmit the acoustic waves 16 into theformation 18, and then fracturing the formation hydraulically. Forexample, this may reduce the overall requirements for the fracturingoperation (e.g., required water volume, pump horsepower, pressure,treatment fluids, etc.).

As other alternatives, the acoustic generator 12 could be operated totransmit the acoustic waves 16 into the formation 18 continuously from awellbore 14 while fracturing operations are conducted from anotherwellbore 22 (e.g., using the system 10 configurations of FIGS. 3 and5-9), or the acoustic generator 12 could be operated alternately withthe fracturing and/or other stimulation operations.

One way that can enhance the excitation from one wellbore 14 to one ormore adjacent wellbores 22 is through pore pressure relief. Whilestimulating via one wellbore, returns may be taken from an adjacentwellbore. This pore pressure relief phenomenon attracts the propagationplane toward that adjacent wellbore. Controlled pore pressure relief canenhance the effect of the acoustic waves 16.

Another application for the concepts of this disclosure isre-fracturing. This would be especially useful in hard-rock formations.After a well is initially fractured, oftentimes the zones need to bere-fractured later in the life of the well due to compaction, plugging,etc. The acoustic generator 12 can be used in a “re-fracturing” systemto excite or re-excite an existing fracture geometry.

Another beneficial use for the acoustic generator 12 is in pin-pointsteam chamber development in steam-assisted gravity drainage (SAGD)wells. A problem in SAGD applications is that the existing lithology,pressure gradients, etc. dictate where the steam chamber developmentoccurs across a long horizontal lateral. It usually occurs somewherenear the toe of the lateral and somewhere near the heal of the lateral.

However, by exciting the reservoir in several places across the lateralsection, the position or areas where the steam chamber develops can beselected or enhanced. An example of this is depicted in FIG. 16, and isdescribed more fully below.

In FIG. 10, the acoustic generator 12 is utilized during a gravelpacking operation in the wellbore 14. During or after a gravel slurry 40is flowed about a well screen 42 connected to the tubing string 34, theacoustic generator 12 is used to transmit acoustic waves into an annulus44 between the screen and the casing 24 (or between the screen and thewellbore 14 if it is uncased) and thereby into a gravel pack 46accumulated in the annulus. This aids in eliminating voids or preventingvoids from forming in the gravel pack 46, and provides a more evenlydistributed gravel pack about the screen 42.

In addition to better distribution and gravel compaction, thenear-wellbore stimulation effect of the acoustic waves removes any skinfrom drilling mud, lost circulation material or perforating damageoccurring prior to the gravel/proppant placement.

In FIG. 11, the acoustic generator 12 is utilized to initiate hardeningor setting of the cement 26 after it has been flowed into the annulus 28surrounding the casing 24. In this manner, the cement 26 does not hardenuntil a point in time when such hardening is desired. Thus, the casing24 can be repositioned, the cement 26 can be circulated out of theannulus 28, operational problems can be resolved, etc., prior toinitiating hardening of the cement. This reduces or entirely eliminatesthe need for adding retardants to the cement 26 to delay full hardeningof the cement.

Capsules or other containers 48 can be used to contain a hardening agent(such as a catalyst) for release into the annulus 28. For example, thecontainers 48 could be exteriorly attached to the casing 24, or thecontainers could be flowed into the annulus 28 with the cement 26.

Suitable containers would be glass bubbles of the type used in drillingmud for density control. Glass bubbles (HGS Series) are available from3M Corporation of St. Paul, Minn. USA. Such glass bubbles could befilled with a catalyst or other hardening agent which causes the cement26 to harden or set when the hardening agent contacts the cement.

When it is desired for the cement 26 to begin hardening, the containers48 are opened by using the acoustic generator 12 to transmit acousticwaves to the containers. The containers 48 could be frangible, so thatthey break open when the acoustic waves are transmitted by the acousticgenerator 12, or the containers could be otherwise configured to openwhen contacted by the acoustic waves.

The acoustic waves 16 can be “tuned” to a resonant frequency of thecontainers 48. Alternatively, the containers 48 could be designed sothat they break or otherwise open when a certain frequency, combinationof frequencies, or combination of stimuli (predetermined frequency orfrequencies, pressure, etc.) are applied to the containers.

Even if the acoustic generator 12 is not used to initiate hardening ofthe cement 26, the acoustic waves 16 transmitted through the cement canstill operate to reduce or eliminate voids and channeling in the cement,and to enhance bonding between the casing 24 and the cement. For thispurpose, the acoustic generator 12 could be “tuned” to generate theacoustic waves 16 at a resonant frequency (or below a resonantfrequency) of the casing 24.

Instead of (or in addition to) the containers 48, the casing 24 could becoated with the hardening agent. The casing 24 could be run into thewell, the cement 26 could be pumped into place in the annulus 28, andthen the hardening agent could be mixed with the cement using theacoustic waves 16 transmitted by the acoustic generator 12.

Thus, the hardening agent can be dispersed and mixed with the cement 26using the acoustic generator 12, no matter what release mechanism (suchas containers 48, coating 49 on casing 24, etc.) is used. The hardeningagent could also be released as a result of heating the cement 26 usingthe acoustic waves 16, as well as simply curing the cement using heatfrom the acoustic waves.

In FIG. 12, the tubing string 34 used to convey the acoustic generator12 into a well is also used to supply fuel 50 and oxidizer 52 to theacoustic generator, in the case where the acoustic generator is of thecombustion type. As depicted in FIG. 12, the fuel 50 is flowed throughan annulus 54 between an outer wall 56 of the tubing string 34 and aninner wall 58. The oxidizer 52 is flowed through a passage 60 extendinglongitudinally through the inner wall 58. Of course, the oxidizer 52could be flowed through the annulus 54 and the fuel 50 could be flowedthrough the passage 60, if desired.

The configuration of FIG. 12 can be used either for transmitting theacoustic waves 16 at a single location in the wellbore 14, or fordisplacing the acoustic generator 12 along the wellbore whiletransmitting the acoustic waves.

In FIG. 13, the acoustic generator 12 is conveyed via a wireline 62,instead of the tubing string 34. The fuel 50 and oxidizer 52 areconveyed into the well along with the acoustic generator 12 (such as, incontainers attached to the acoustic generator, etc.). This provides aself-contained acoustic wave generating system which is well suited fordistributing acoustic waves over long distances along a wellbore, or forgenerating acoustic waves at one or more discrete locations along awellbore.

In FIG. 14, the acoustic waves 16 transmitted into the formation 18 aredetected in the adjacent wellbore 22 by an array of sensors 64distributed longitudinally along the wellbore. The sensors 64 may be ofthe type used in seismic imaging (e.g., the sensors could be geophones,hydrophones, accelerometers, or other types of sensors). In this manner,tomography of the formation 18 (e.g., to detect the presence and extentof fluid interfaces, fractures, faults, lithology, etc.) can be readilyperformed. It is contemplated that the presence and location of anotherwellbore, a drill string, etc. can even be detected using the acousticgenerator 12 and sensors 64.

The acoustic generator 12 can be used in conjunction with vibratorysource profiling or seismic profiling. The acoustic generator 12 can bedisplaced along the wellbore 14 while transmitting the acoustic waves 16into the formation 18, if desired. The sensors 64 may alternatively bepositioned at the earth's surface or sea floor, or in the wellbore 14.

The acoustic generator 12 may provide for mid-range imaging about thewellbore 14 (for example, greater than a meter from the wellbore), andthe sensors 64 could be included with the acoustic generator or conveyedtherewith, to provide a useful acoustic imaging tool.

In FIG. 15, the tubular string 34 used to convey the acoustic generator12 is a drill string. The wellbore 14 is being drilled as the acousticgenerator 12 is transmitting the acoustic waves 16 into the formation18. With the acoustic generator 12 positioned near the end of the drillstring 34 (e.g., close above a drill bit 66 being used to drill thewellbore 14), the acoustic waves 16 can even be transmitted ahead of thebit, so that characteristics of the formation 18 ahead of the bit can bedetermined. Such characteristics can include presence and extent offluid interfaces, fractures, faults, lithology, permeability, porosity,fluid type, etc.).

In FIG. 16, one or more acoustic generators 12 are used in asteam-assisted gravity drainage (SAGD) system. As depicted in FIG. 16,multiple acoustic generators 12 are positioned in the wellbore 14 usedfor injecting steam 70 into the formation 18.

The acoustic waves 16 generated by the acoustic generators 12 assist thesteam 70 in penetrating the formation 18, so that a steam chamber 72 isformed with a desired shape and extent. As discussed above, it is commonfor a steam chamber to develop preferentially near the heel and toe of aSAGD injection wellbore

However, using the principles of this disclosure, the shape and extentof the steam chamber 72 can be controlled as desired, for example, toenhance development of the steam chamber between the heel and toe (or atany other location, such as an area of relatively low permeability,etc.) along the wellbore 14. Any number, combination, spacing, etc., ofthe acoustic generators 12 may be used. Furthermore, the acousticgenerators 12 may be used only in an injection wellbore (as depicted inFIG. 16), only in a production wellbore, or in a combination ofinjection and production wellbores.

In each of the above examples, the optimum acoustic characteristics(e.g., frequency, amplitude, duration, pulsing, frequency sweeps,multiple simultaneously transmitted frequencies, etc.) will be chosenfor each operation. In the case of enhancing sweep efficiencies inconformance operations, optimum frequencies could provide a conductivitymanagement system to enhance ultimate hydrocarbon recovery. As analternative to hydraulic fracturing, micro-seismic monitoring technologycould be deployed as a means to quantify and tune the effects andcoverage of the acoustic energy field. In cementing operations, theup-hole cementing designs will preferably be engineered to withstand theacoustic energy output that is produced within the targeted hydrocarbonbearing reservoirs.

One of the possible benefits of the acoustic generator 12 is to reduceor eliminate the need for hydraulic fracturing. Another possible benefitis to excite the natural matrix in a hydrocarbon bearing formation 18 inorder to enhance placement of treating chemicals and/or to increasehydrocarbon recovery from a reservoir. The acoustic wave generationprocesses should be an effective alternative to current technologiesused in these types of applications.

Preferably, the acoustic generator 12 may have an acoustic power outputof around 250 dB. Preferably, the acoustic generator 12 has a tunableoutput frequency, and may have multiple simultaneous frequency outputs.It is contemplated that acoustic frequencies in the hundreds of Hertzmay be most useful for exciting the rock matrix of the formation 18, butit should be clearly understood that other frequencies may be used inkeeping with the principles of this disclosure.

The acoustic energy may be used near a zone of production, or higher inthe wellbore, semi-permanently for inhibition or as an intervention forremediation, for flow assurance problems such as hydrates, scale, wax,or asphaltine formations, in the near well production zone or in thecompletion or tubulars in the well.

The acoustic generator 12 may be capable of transmitting information(e.g., data, commands, etc.) as part of a telemetry system. For example,the acoustic generator 12 could transmit data regarding pressure,temperature, flow, formation characteristics, etc. during a stimulation,fracturing, treatment, conformance, production or drilling operation.

The data could be transmitted via frequency modulation (e.g., wherein a0 bit is transmitted as one frequency, and a 1 bit is transmitted asanother frequency), binary pulsing (e.g., wherein a 0 bit is indicatedby presence of a frequency, and a 1 bit is indicated by absence of thatfrequency), or tone burst length modulation (e.g., wherein a 0 bit isindicated by transmission of a frequency for a predetermined timeperiod, and a 1 bit is indicated by transmission of the frequency foranother predetermined time period), or any other data modulationtechnique.

When being used to stimulate fluid flow in the formation 18, theacoustic generator 12 preferably provides sustained high frequencyexcitation. Excitation at a resonant frequency of the formation 18 withimpedance matching may provide maximum energy transfer to the formation.Resonant frequencies of other elements of the system 10 may also be used(for example, resonant frequencies of the perforations 32, casing 24,containers 48, proppant particles in a fracturing operation, etc., orbelow such resonant frequencies), multiple resonant frequencies may betransmitted simultaneously or separately, and harmonic frequencies maybe transmitted.

Resonant frequencies of the system 10 can be determined by transmittinga sweep of frequencies from the acoustic generator 12 and analyzing theresponse of the system. For example, the acoustic signal strength couldbe monitored from an adjacent wellbore, and maximum signal strengthcould correspond to maximum transmission of acoustic energy through theformation 18, whereas minimum signal strength could correspond tomaximum absorption of acoustic energy by the formation. In someoperations (such as data communication, formation tomography, etc.)maximum transmission of acoustic energy may be desirable, whereas inother operations (such as stimulation, conformance, etc.) maximumabsorption of acoustic energy may be desirable.

The acoustic generator 12 may be “tuned” using other methods, as well.For example, where the acoustic waves 16 are transmitted in order toenhance production of fluid 20 from a formation 18 (such as, in any ofthe configurations of FIGS. 1-9 and 16), the acoustic generator 12 maygenerate multiple frequencies (or a sweep of frequencies) over time, andthe production which results from these frequencies can be evaluated tosee which frequency or frequencies generate(s) a maximum rate ofproduction.

Metrics other than rate of production may be used to select an optimumfrequency or frequencies for the acoustic waves 16. For example, aminimum ratio of drawdown or pressure differential from the formation 18to the wellbore 14 or 22 to rate of production (drawdown/productionrate), a minimum skin, and other metrics may be analyzed to indicatewhich frequency or frequencies should be transmitted by the acousticgenerator 12 for optimum production results.

It may now be fully appreciated that the above disclosure provides manyadvancements to the art. In one example, the disclosure provides a wellsystem and associated method in which an acoustic generator is used toexcite a formation with acoustic waves transmitted from the acousticgenerator.

The formation may be excited by the acoustic waves while a fluid isflowed into the formation. The fluid may include at least one of astimulation fluid, a conformance fluid, a fracturing fluid and atreatment fluid.

The formation may be excited by the acoustic waves and then fluid (suchas a hydrocarbon fluid) may be produced from the formation.

The acoustic waves may be transmitted at a resonant frequency of thesystem. The acoustic waves may be transmitted at a resonant frequency ofthe formation and/or a resonant frequency of an element (such as acasing, perforation, etc.) of the system.

The acoustic generator may be positioned in one wellbore, and fluid maybe produced from the formation into another wellbore.

The acoustic waves may be transmitted into the formation from onewellbore, and the acoustic waves may be detected by at least one sensorpositioned in another wellbore, at the earth's surface, at a sea floor,or in the first wellbore. Detection of the acoustic waves by the sensorsprovides indications of formation characteristics, such as presence andextent of fluid interfaces, fractures, faults, lithology, permeabilityand porosity.

The acoustic generator may be supplied with fuel and oxidizer via atubing string, via lines interconnected to the acoustic generator, orvia chambers conveyed with the acoustic generator.

The acoustic waves may be generated via combustion in the acousticgenerator, generated hydraulically or generated electrically.

The acoustic generator may be positioned in a wellbore permanently ortemporarily.

The acoustic waves may be detected and information may be therebytransmitted, with the information including at least one of data andcommands.

The acoustic waves may be transmitted into the formation from onewellbore, and fluids may be produced from the formation from at leastone other (second) wellbore. There may be multiple second wellborespositioned about the first wellbore.

The first and second wellbores may be generally horizontal or at leasthighly deviated. The first and second wellbores may be multilateralwellbores. The first and second wellbores may be positioned laterallyadjacent each other.

The well system can include at least one sensor 33 which measures aresponse of the well system to the transmitted acoustic waves. Theacoustic generator may transmit the acoustic waves at a frequency whichmaximizes the well system response.

The acoustic generator may transmit the acoustic waves at a frequencywhich maximizes production of fluid from the well system, at a frequencywhich minimizes skin in the well system, and/or at a frequency whichminimizes a pressure differential from the formation to a wellbore for agiven rate of production.

The acoustic waves may be used to increase development of a steamchamber in the formation.

Also provided by the above disclosure is a well system and associatedmethod in which an acoustic generator transmits acoustic waves intocement surrounding a casing. The acoustic waves may cause at least onecontainer to open, thereby initiating hardening of the cement. Openingof the container may release a hardening agent, such as a catalyst, intothe cement. The container may be attached to the casing, or thecontainer may be flowed into an annulus between the casing and awellbore with the cement.

The acoustic waves may reduce or eliminate voids and/or channeling inthe cement. The acoustic waves may provide for even distribution andbonding of the cement about the casing.

The acoustic waves may be transmitted at a frequency which is equal toor less than a resonant frequency of the casing. The resonant frequencymay be in a radial or transverse mode of vibration of the casing.

The acoustic waves may be transmitted at a frequency which maximizesacoustic energy transfer to the cement.

The acoustic waves may be transmitted at a frequency which maximizes anoutput of a sensor 33 which senses a response to the acoustic waves.

Also described above is a well system and associated method in which anacoustic generator is used to transmit acoustic waves into an annulussurrounding a well screen during or after a gravel packing operation.The acoustic waves may operate to reduce voids in a gravel pack in theannulus. The acoustic waves may provide for even distribution of agravel pack about the well screen.

The acoustic waves may be transmitted at a frequency which is equal toor less than a resonant frequency of the well screen. The resonantfrequency may be in a radial or transverse mode of vibration of the wellscreen.

The acoustic waves may be transmitted at a frequency which maximizesacoustic energy transfer to a gravel pack in the annulus.

The acoustic waves may be transmitted at a frequency which maximizes anoutput of a sensor 33 which senses a response to the acoustic waves.

Also described above is a well system and associated method in which anacoustic generator is connected in a drill string in close proximity toa drill bit, the acoustic generator transmitting acoustic waves into aformation ahead of the bit. Characteristics of a portion of theformation ahead of the bit may be detected prior to the bit cutting intothe portion of the formation. The formation characteristics may compriseat least one of presence and extent of fluid interfaces, fractures,faults, permeability, porosity, lithology, a wellbore or another drillstring.

Also described above is a well system and method in which acoustic wavesare transmitted into a formation during a fracturing process whichincludes proppant, increasing depth of penetration and/or density ofproppant (e.g. sand, ceramics, etc.) flowed into the fracture(s),resulting in increased or deeper propping and increased conductivity ofthe propped fracture(s).

Also described above is a well system and method in which acoustic wavestransmitted into a formation increase wetting and mixing of conformanceagents such as relative permeability modifiers, thereby improvingrejection of water and/or gas from entry to the near wellbore region orfractures in the formation and improving oil production or productionratios (hydrocarbons/water or oil/water).

Also described above is a well system and method in which acoustic wavesare transmitted into a formation near a zone of production or higher,semi-permanently for inhibition or as an intervention for remediation,of flow assurance problems such as hydrates, scale, wax, or asphaltineformations, in the near well production zone or in a completion ortubulars.

Also described above is a well system and method in which a casing iscoated with a hardening agent. The casing is run into the well, thecement is pumped into place in an annulus, and then the hardening agentis mixed with the cement using acoustic waves transmitted by an acousticgenerator.

Also described above is a well system and method in which a hardeningagent is dispersed and mixed with a cement using an acoustic generator,no matter what release mechanism is used.

Also described above is a well system and method in which a hardeningagent is released as a result of heating a cement using acoustic waves,and/or curing the cement using heat from the acoustic waves.

Also described above is a well system and method in which, whilestimulating via one wellbore, returns are taken from an adjacentwellbore, whereby pore pressure relief attracts a propagation planetoward the adjacent wellbore. Controlled pore pressure relief canenhance the effect of the acoustic waves.

Also described above is a well system and method in which, after a wellis initially fractured, an acoustic generator is used to excite orre-excite an existing fracture geometry.

Also described above is a well system and method in which a formation isexcited by acoustic waves generated by an acoustic generator in severalplaces across a generally horizontal wellbore, whereby the position orareas where a steam chamber develops in a SAGD system is selected.

It is to be understood that the various examples described above may beutilized in various orientations, such as inclined, inverted,horizontal, vertical, etc., and in various configurations, withoutdeparting from the principles of the present disclosure. The embodimentsillustrated in the drawings are depicted and described merely asexamples of useful applications of the principles of the disclosure,which are not limited to any specific details of these embodiments.

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments,readily appreciate that many modifications, additions, substitutions,deletions, and other changes may be made to these specific embodiments,and such changes are within the scope of the principles of the presentdisclosure. Accordingly, the foregoing detailed description is to beclearly understood as being given by way of illustration and exampleonly.

What is claimed is:
 1. A well system, comprising: an acoustic generatorwhich transmits acoustic waves into cement surrounding a casing; and atleast one container which opens in response to the transmitted acousticwaves, wherein a hardening agent is released in response to the openingof the container.
 2. The well system of claim 1, wherein the containeris attached to the casing.
 3. The well system of claim 1, wherein theacoustic waves reduce voids in the cement.
 4. The well system of claim1, wherein the acoustic waves reduce channeling in the cement.
 5. Thewell system of claim 1, wherein the acoustic waves evenly distribute thecement about the casing.
 6. The well system of claim 1, wherein theacoustic waves promote bonding of the cement to the casing.
 7. The wellsystem of claim 1, wherein the acoustic waves are transmitted at afrequency which is equal to or less than a resonant frequency of thecasing.
 8. The well system of claim 7, wherein the resonant frequency isin a radial mode of vibration of the casing.
 9. The well system of claim7, wherein the resonant frequency is in a transverse mode of vibrationof the casing.
 10. The well system of claim 1, wherein the acousticwaves are transmitted at a frequency which maximizes acoustic energytransfer to the cement.
 11. The well system of claim 10, wherein theacoustic waves are transmitted at a frequency which maximizes an outputof a sensor which senses a response to the acoustic waves.
 12. The wellsystem of claim 1, wherein the hardening agent is dispersed and mixedwith the cement by the acoustic waves.
 13. The well system of claim 1,wherein the hardening agent is released as a result of heating thecement using the acoustic waves.
 14. The well system of claim 1, whereinthe cement is cured with heat generated by the acoustic waves.
 15. Awell system, comprising: an acoustic generator which transmits acousticwaves into cement surrounding a casing, wherein at least one containeropens in response to the transmitted acoustic waves, and wherein thecontainer is flowed into an annulus between the casing and a wellborewith the cement.
 16. A well system, comprising: an acoustic generatorwhich transmits acoustic waves into cement surrounding a casing; and atleast one container which opens in response to the transmitted acousticwaves, wherein the casing is coated with a hardening agent, the casingis run into the well, the cement is pumped into place in an annulussurrounding the casing, and then the hardening agent is mixed with thecement using the acoustic waves transmitted by the acoustic generator.